sched_ext tasks currently are starved by RT hoggers especially since RT
throttling was replaced by deadline servers to boost only CFS tasks. Several
users in the community have reported issues with RT stalling sched_ext tasks.
Add a sched_ext deadline server as well so that sched_ext tasks are also
boosted and do not suffer starvation.

A kselftest is also provided to verify the starvation issues are now fixed.

Link to v1: https://lore.kernel.org/all/20250315022158.2354454-1-joelagnelf@nvidia.com/

Changes in v2:
 - Fixed a hang related to using rq_lock instead of rq_lock_irqsave.
 - Added support to remove BW of DL servers when they are switched to/from EXT.

Andrea Righi (1):
  selftests/sched_ext: Add test for sched_ext dl_server

Joel Fernandes (9):
  sched: Add support to pick functions to take rf
  sched: Add a server arg to dl_server_update_idle_time()
  sched/ext: Add a DL server for sched_ext tasks
  sched/debug: Fix updating of ppos on server write ops
  sched/debug: Stop and start server based on if it was active
  sched/debug: Add support to change sched_ext server params
  sched/deadline: Clear the defer params
  sched/deadline: Add support to remove DL server bandwidth
  sched/ext: Relinquish DL server reservations when not needed

 include/linux/sched.h                         |   2 +-
 kernel/sched/core.c                           |  19 +-
 kernel/sched/deadline.c                       |  85 +++++--
 kernel/sched/debug.c                          |  96 ++++----
 kernel/sched/ext.c                            | 108 ++++++++-
 kernel/sched/fair.c                           |  15 +-
 kernel/sched/idle.c                           |   4 +-
 kernel/sched/rt.c                             |   2 +-
 kernel/sched/sched.h                          |  13 +-
 kernel/sched/stop_task.c                      |   2 +-
 tools/testing/selftests/sched_ext/Makefile    |   1 +
 .../selftests/sched_ext/rt_stall.bpf.c        |  23 ++
 tools/testing/selftests/sched_ext/rt_stall.c  | 213 ++++++++++++++++++
 13 files changed, 502 insertions(+), 81 deletions(-)
 create mode 100644 tools/testing/selftests/sched_ext/rt_stall.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/rt_stall.c

CC: Joel Fernandes joelagnelf@nvidia.com
CC: Ingo Molnar mingo@redhat.com
CC: Peter Zijlstra peterz@infradead.org
CC: Juri Lelli juri.lelli@redhat.com
CC: Vincent Guittot vincent.guittot@linaro.org
CC: Dietmar Eggemann dietmar.eggemann@arm.com
CC: Steven Rostedt rostedt@goodmis.org
CC: Ben Segall bsegall@google.com
CC: Mel Gorman mgorman@suse.de
CC: Valentin Schneider vschneid@redhat.com
CC: Tejun Heo tj@kernel.org
CC: David Vernet void@manifault.com
CC: Andrea Righi arighi@nvidia.com
CC: Changwoo Min changwoo@igalia.com
-- 
2.43.0